OK, now for the fun part.
One of the reasons I was interested in this tractor is to take apart
a modern
HST. The good news here is that the
HST is OK, and needs
nothing. There is a separate filter for the
HST, which protected it from
the puree of broken metal fragments that came out of the main gearbox
and rear end.
First photo shows the main components of the
HST. The motor and the
pump are virtually identical. The pump varies its displacement with
a variable angle swash plate. The motor uses a fixed swash plate.
The tube with the O-rings in the middle is where the
MFWD drive shaft
passes thru the
HST on its way to the main gearbox. Oil in the
HST
does not mix with that in the gearboxes until after filtration. Nice.
2nd photo shows the cylinder block and pistons. Note the hole in the
brass "slipper", that rubs against the swash plate. That supplied lube
to the plate, and, of course, contributes to some of the inefficiencies
of a
HST.
Finally, I miked everything and nothing was out of spec. One bit of
good news. I replaced the main shaft ball bearings anyway (they are
cheap).
Next: charge pump and main gearbox